The present invention relates to a composition for use in forming a thick film resistive type oxygen sensing element and a method of forming thick film oxygen sensors adapted for use in automotive exhaust systems.
Resistive type oxygen sensors are based on the ability of certain oxides, such as titanium dioxide, to exchange oxygen with the surrounding environment. As oxygen is gained or lost from the oxide, the resistivity, and conversely the conductivity of the oxide is altered, and measurement of the resistivity can be used as a means for measuring the oxygen content of an exhaust gas within which the sensing element is situated. Examples of such sensing elements are given in U.S. Pat. No. 4,066,413 and U.S. Pat. No. 4,007,435, as well as discussions of the function of the resistive type sensor material and problems associated with measurement of the oxygen content of automotive exhaust. Discrete types of titanium dioxide resistive sensors have also been disclosed, for example in U.S. Pat. No. 4,147,513, assigned to the assignee of the present invention, the contents of which are incorporated herein, but the use of platinum wire leads renders the discrete sensor expensive and difficult to manufacture, as well as subject to mechanical damage.
By use of the present invention, resistive type oxygen sensors are formed which are structurally sound, readily manufactured, and relatively inexpensive.